Pipe bending machine



Aug. 15, 1967 E. E. CUMMINGS PIPE BENDING MACHINE 5 $heets$heet 1 Filed Nov. 6, 1964 I-I-LI .|RE@ .I WI.I-

5. f. CU/77 77/fl9J INVENTOR.

BY M

ATTORNEY 15, 1967 E. E. CUMMINGS 3,335,588

PIPE BENDING MACHINE Filed Nov. 6, 1964 5 Sheets-Sheet :2

INVENTOR. f. E. fu/rr/zw/zgJ ATTORNEY ll l V I N digiy- N g- 15, 1967 E. E. CUMMINGS 3,335,588

PIPE BENDING MACHINE Filed Nov. 6, 1964 5 Sheets-Sheet 5 f. 5. 6007/77/09: INVENTOR.

BY 4Q haw a ATTOR United States Patent 3,335,588 PIPE BENDING MACHINE Ernest E. Cummings, Houston, Tex., assignor to Crutcher- Rolfs-Cummings, Inc., Houston, Tex., a corporation of Texas Filed Nov. 6, 1964, Ser. No. 409,484 13 Claims. (CI. 72-28) ABSTRACT OF THE DISCLOSURE An apparatus for cold bending of steel tubing such as constitute end to end joint sections in a cross-country pipe line, which pipe are generally of large diameter. The apparatus is adapted for field use whereby the pipe can be bent at the point of installation in the pipe line, for example.

This invention relates to the cold bending of steel tubing such as constitute end to end joint sections in a cross-country pipe line and more particularly to a bending machine for operating on currently favored thin wall, high strength alloy, large diameter pipe and for transportation along the pipe line right of way and especially when the terrain is rough and requires many turns.

An object of the invention is to provide a self contained bending assembly of relatively small bulk, both transversely and vertically, and of minimum weight for ease of transit whether in sometimes close quarters along the path to be followed in laying a line or in rail or road travel to and from work locations.

Another object of the invention is to provide a bending machine wherein a holding shoe is longitudinally rearwardly offset from the bending die and a long stiff straight back has its rearward end portion in opposing facing relation to the curved die face and has its forward end portion projected beyond the die for a long distance and wherein the long stiff back which carries and backs up a length of straight pipe ahead of the bending zone, is rocked for a progressive bending action on a short extent of pipe against a small die area and with force applied to the stiff back at opposite end connections of which the rear connection is spaced behind the center of the die for a continuous squeeze clamping of the pipe toward the die face but with a snubbing pressure which accommodates back off of the stiff back portion rearwardly of the bend zone after the bending operation has begun and the zone of bending advances on succeeding increments of pipe length and as pipe wall contact and conformation to the curved die face progressively increases.

A further object is to provide a bending machine as aforesaid in which the convex die face curvature, determinative of the bending arc, recedes or diverges upwardly in both of opposite directions away from a midpoint in the length thereof and only a forward relatively small fraction of such length is active for bending contact while the rearward remaining major portion of the curved face affords a bearing seat for preceding bends during subsequent bending operations and the pipe wall on the inner side of such preceding bends is braced tightly against the curved seat by controlled positioning of the stiff back whereby to smooth out and minimize wave formations from longitudinal compressive stress within the bent zones of the pipe wall.

A still further object is to provide a holding shoe with a co-operating pipe embracing clamp for backing up the pipe wall throughout substantially its entire circumference so as to maintain pipe wall circularity and resist inward wall out-of-round collapse while bending force "ice is being applied on a region of the pipe just ahead of the bending shoe.

Other objects will appear from the following specification and the accompanying drawing wherein FIG. 1 is a side elevation of a bending machine embod n'ng the subject matter of this invention;

FIG. 2 is a front elevation looking in the direction of the arrows on line 2-2 of FIG. 1;

FIG. 3 is a transverse section through the holding die assembly as on line 3-3 of FIG. 1;

FIG. 4 is a side view partly in section of the principal bending components prior to the performance of a bending operation;

FIG. 5 is a view similar to FIG. 4 but illustrating the relative position of the components at the end of the last of a succession of several bends on adjoining increments of pipe-length; and

FIG. 6 is a schematic drawing of a hydraulic actuating system.

Referring to the drawings, a vehicular type bending machine is illustrated as including a main frame 1 made up of welded together I-beams to provide a pair of vertical side trusses connected at intervals by crossmembers 2-2. Each side truss comprises a long lower beam 3 with front and rear upwardly converging rails 4 and 5 supporting a top beam 6. Each side of the main frame is supported from the ground by running gear such as an endless track assembly 7 at the rear of the frame and front bearing runner-s 8. A forward tongue 9 is for coupling to a towing vehicle.

For the performance of a pipe bending operation in a vertical plane and about a center point high above the machine whereby the pipe wall portion on the inside of the bend and of shorter bend radius is uppermost, there is mounted within the main frame 1 a set of co-operating pipe engaging members arranged in longitudinal succession for alternate contact with diametrically opposite top and bottom sides of a pipe inserted between the upper and lower members. From front to rear, these members are a relatively long stiff back 10 having a pipe receiving semicylindrical pocket in its upper face, a bending die 11 of a length many times greater than the length of a bend to be formed in each operating cycle and whose underside has a downwardly facing die cavity presenting a pipe engaging face that is semicircular in transverse section and is longitudinally curved in longitudinal section on the arcuate path to which a pipe bend will conform and a relatively short holding shoe 12 having an upwardly facing semicylindrical pipe bearing contact. The half-round pipe receiving surfaces of the holding shoe 12, the bending die 11 and the stiff back 10 are each of substantially the same radius as the external pipe surface so as to closely fit and hold the contacted tubular wall shape against harmful deformation under stress incident to force application of a bend forming operation. For convenience, the pipe engaging surfaces usually are provided with replaceable liners sized for whatever pipe diameters and the liners are nested within the several pipe receiving cavities as shown, for

example, at 12a in FIG. 3.

As here involved, the holding shoe 12 is spaced rearwardly from the bending die and is a vertically shiftable boxlike body pivoted to rock about a transverse axis.

In its lower position of rest as seen in FIG. 1, the bottom edges of its two side plates bear on an upwardly and rearwardly inclined top face of the rearmost crossmemher or members 2. Mounted by these side plates, as seen in FIG. 3, are the opposite ends of a rock shaft 13 for a bearing plate 14 which is to seat downwardly on a set of three longitudinally slidable and rearwardly tapered wedges 15 arranged side by side between. the bearing 14 and the upper inclined face of the rearmost crossmember 2. In power transmitting relation with the wedges is a fluid pressure responsive motor consisting of a piston and cylinder assembly 16 hinged at opposite ends to the wedges and to the machine frame so that controlled actuation of the power cylinder projects and retracts the wedges for adjustably setting the height of the holding shoe 12.

Another pressure fluid responsive cylinder motor 17 extends between and is joined at opposite ends to the upper terminals of a pair of arcuate clamping jaws 1818 which are hinged to the side of the holding shoe 12 for co-operation therewith in closing around the top side of a pipe and substantially completing the full encirclement of and thereby bracing the pipe wall throughout its entire circumference. This arrangement will be particularly useful in stiffening the pipe wall against out-of-round collapse during the initial first and second of a series of pipe bending steps. Following each of the initial bending operations, the pipe will have been shifted rearwardly and the length of rearward pipe projection behind the bent region will have been increased as the previously bent increments of pipe length approach the holding shoe, and there will be less need for complete pipe embracement and radially inward backing pressure on the upper half of the tubular wall in the holding shoe.

The bending die 11 is fixedly suspended a short distance ahead of the holding shoe by being bolted at its front and rear to the two top frame crossmembers 2.

The longitudinal curvature of the die face is such that the face recedes equally in fore and aft directions from its midpoint, which is to say that the center of the arc of convex curvature is on a line A projected from the center of and normal to a chord which intersects opposite ends of the die face. Only a relatively small area immediate the front of the die face is employed for the bending action on the pipe wall. For example, in a commercial embodiment, such bending area extends through approximately a twelve-inch fraction of a five-foot long die.

Also, in the commercial machine, the stiff back is approximately fourteen feet long for properly backing up and stiffening a considerable portion of the pipe wall on the front side of the arc of bending and the major portion of the stiff back length projects forwardly of the die while its rearward end portion for about three and a half feet underlies the bending die. Such rearward portion terminates behind the longitudinal die center on the line A and is suspended rearwardly of the die center point on the side thereof toward the holding shoe, by a piston and cylinder motor assembly 19, one at each side of the machine. Each motor 19 is pivotally connected at top and bottom on transversely disposed axes with the upper frame beam 6 and with the end portion of the stiff back 10 which is adjacent and nearer to the holding shoe. These points of connection are indicated in FIG. 1 as being on a vertical line B. In operation, the rearward stiff back portion raises a pipe placed therein toward the bending die and not only backs up the tubular wall but maintains a proper squeeze pressure on the wall region being pushed progressively around the die face bending curvature while coincidently accommodating a backing away action of the stiff back rearwardly from the point of bend deformation so as to provide relief of pressure concentration on the pipe wall rearwardly on the region undergoing bending stress. For maximum leverage, a large power cylinder and piston motor 20 is provided on each side at the front of the stiff back and in response to fluid pressure delivered into either of opposite ends of the cylinder, the stiff back is raised or lowered about its rear pivotal connection with the power cylinder 19. Controlled elevation at the front of the stiff back is usually in the range of about twelve inches for an initial bending stroke and increases to about fourteen inches for the next bend and increases up to about eighteen inches on subsequent twelve-inch bend length increments to the completion of a specified bend to given angularity between the ends of a particular joint of pipe. Each of the front power cylinders 20 is pivotally connected on transverse axes at the lower end to a frame bracket and at the upper end to a pair of side straps 21 welded at front and rear edges to vertical plates 22 which in turn are welded to and project laterally from the side of the stiff back.

A series of transversely extending rollers 23 are carried in the frame 1 in longitudinally spaced apart relation, one at each end of the frame and one at an intermediate location between the stiff back and the holding shoe. These rollers project above the bottoms of the pipe engaging depressions in both the stiff back and the holding shoe at their lowered positions of rest so that the pipe can be brought into the machine and rolled forward for properly positioning its area to be bent. A cable 24 leading from the drum of a winch 25 is then tied to a forward portion of the pipe. Such winch assembly is supported by one of the frame crossmem-bers 2 and includes a pressure fluid driven reversible motor whose actuation between successive bending operations pulls the pipe backward for bringing a new length increment into position for a bend-working performance thereon.

The motor of the winch 25 and each of the pressure responsive motors 16, 17, 19 and 20 are supplied from a pressure source powered by an internal combustion engine 26 and controlled at the operators station or console 27 having a group of hand lever actuated valves 28, 29, 30 and 31, each having a neutral or off setting and two other settings for alternate delivery and return of fluid to and from selected sides of the several motors, as can best be seen in the schematic showing of FIG. 6. In this case, the engine 26 drives a large liquid pump 32 capable of building pressure to twenty-two hundred pounds and a smaller liquid pump 33 to supply pressure up to thirteen hundred pounds. Both pumps have suction connections to withdraw hydraulic liquid through a filter 34 and from a storage reservoir or sump 35. The pump 32 has pressure supply line connections 36 to both of the manual valves 28 and 29 and the pump 33 has pressure supply line connections 37 to both of the manual valves 30 and 31. Return line connections 38 to the sump run from the two manual valves 28 and 29 and return line connections 39 go to the sump from both valves 30 and 31. In one delivery setting of the manual valve 28, pressure fluid travels through a connecting conduit 40 to the winch motor for forward drive when return flow from the motor is through a connecting pipe 41. In the other delivery setting of the manual valve 28, return flow will be through the conduit 40 while fluid pressure moves through the conduit 41 for winch reverse drive. Similarly, between the hand valve 29 and the opposite ends of the bending cylinder 20, there are two connecting flow lines 42 and 43, each for directing liquid from the pump 32 or to the sump 35 according to alternate hand valve settings for piston projection in one instance and for piston retraction in the other setting. In like manner, the wedge actuating cylinder and piston assembly 16 will be projected when one end of the cylinder is vented to the sump through the line conduit 44 and the hand valve 31 and upon delivery of pressure fluid to the opposite end of the cylinder through a line 45 leading from the hand valve 31 and containing a back flow check valve 46. The purpose of the check valve 46 is to enable the hand valve 31 to be placed in neutral position with fluid locked within the cylinder 16 for maintaining the holding shoe lift wedges 15 in any position to which they have been set. Retraction of the wedges is obtained by the alternate setting of the hand valve 31 to pressurize the line 44 as well as a branch line 47 for the application of opening force on the check valve 46, whereupon the back end of the cylinder is vented through the line 45, the hand valve 31 and the return conduit 39. Joined to the hand valve 30 are conduits 48 and 49, to be alternately vented and pressurized, and the conduit 49 is branched for concurrent communication with the piston projecting ends of the cylinders of both the clamp motor unit 17 and the squeeze motor unit 19. The opposite or piston retracting ends of these cylinders both communicate with branches of the conduit 48 and pressurization of this conduit affords the working strokes in the retracting direction.

The branch of the conduit 48 to the clamp cylinder 17 contains a stop cock 50 which is open during the first few stiff back strokes, after which the clamp abutment action as previously mentioned can be discontinued dur ing additional bending sequence by closing the stop cock 50. Complete venting of the conduit is through the hand valve 30 but pressure in the line is kept below a desired level by pressure relief through a sump connection 51 containing an adjustable relief valve 52 which opens in response to line pressure above a selected value for which the relief valve has been preset. Presetting is according to predetermined relative working pressures at the piston projecting end of the bending cylinder 20 and at the piston retracting end of the squeeze cylinder 19. For checking such pressure diflierentials, a pressure gauge 53 in the pressure line 42 and a pressure gauge 54 in the pressure line 48 can be located at the operators station 27. Relief of actuating pressure within the squeeze cylinder 19 when its liquid is trapped in the neutral setting of the hand valve 30, is desirable to allow the rear end of the stiff back to back off or descend slightly away from the pipe in the continuing rise of the stiff back front end and for bracing successive length increments of the pipe against the receding working face curve of the bending die. With the stiff back bearing on the pipe wall ahead of the rearwardly projecting stiff back portion, an increased load will be applied in the direction of an outward pulling on the piston in opposition to the liquid entrapped within the cylinder unit 19, and to avoid undue stress on the machine and any added burden on the bending cylinder unit while maintaining the rear end of the stiff back under proper snubbing and squeezing pressure toward the bending die, the valve 52 automatically eliminates from the cylinder 19 the liquid pressure in excess of what is needed for properly locating the back end of the stiff back.

For the performance of the initial one of a succession of bend forming steps, the holding shoe 12, either alone or concurrently with the front of the stiff back, is raised a short distance sufficient to lift the previously introduced pipe above the supporting rollers 23. It may be here mentioned that conventional bending machines of the general type here involved usually have pointers or markers operating over scales at the operators station and connected one with the holding shoe and the other with the stiff back for indicating at all times their respective heights and thus guiding the manual valve control of pressure application and cutoff. With the pipe resting in the holding shoe, the stop cock 50 is next opened and the valve 30 is actuated for the closure of the clamping arms 18 over the top of the pipe. At the same time, the squeeze cylinder 19 will be contracted to lift the rear of the stiff back and the parts will be in the relationship somewhat as shown in FIG. 4. At any the wedge 15 should now be retracted and the cylinder 19 projected to drop the back end of the pipe and the stiff back for inclination of the pipe forwardly and upwardly for presenting the tube wall nearly tangent to the die cavity just behind the rearward end of the twelveinch long effective bending surface at the front portion of the die. Thereupon pressure application for raising the front end of the stiff back will first push the pipe wall into transverse line contact with the receding face of the curved die at about eleven inches rearwardly of its front end and thereafter successive increments of the pipe wall will be progressively pushed against the die face until completion of the bend in a twelve-inch long section of pipe. Upon release of the clamping arms 18 and a dropping of both the holding shoe and the stiff back below the rollers 23, the cable winch 25 will pull the pipe back a distance on the order of twelve inches, whereupon the next bending operation can take place. Pipe portions rearwardly and forwardly of the completed bend will be in slightly angular relation after the initial bend and in compensation therefor the height of the holding shoe will be raised slightly more than it was during the first bend and the previously bent region of the pipe will seat itself against the curved die face in the area extending generally between twelve inches and twenty-four inches from the forward end of the die: when the stiff back is again raised. In the second bending stroke, another twelve-inch increment of pipe length will be conformed to the die curvature and similarly a like bend will be performed in each subsequent bending operation until eventually the length of bend will correspond with or even exceed the length of the bending die so that the bent pipe will fit against the die curvature throughout its entire length, as seen in FIG. 5. Actuation of the wedges 15 at the start of each bending stroke will be such as to raise the holding shoe to whatever height is required for properly positioning the pipe and the contact of the die with the previously bent wall portions will tend to smooth out wave formations and resist compressive stresses in the top wall which might otherwise result in wall deformation. Further to reduce wall collapse, there may be employed an internal expanding mandrel for insertion axially and outwardly bearing on the wall of the pipe at the location of the bending die.

The foregoing consists of a specific description of a preferred embodiment of the improved bending machine and it is to be understood that such modifications and variations may be made as come within the scope of the appended claims.

What is claimed is:

1. In a pipe bending machine having a pair of members projected longitudinally of a pipe to be received between the members, one member presenting a pipe engaging die face curved longitudinally and outwardly from the center point thereon for pipe bend conformation thereto and the other member being a longitudinally straight stiff back having its opposite end portion spaced in opposite directions longitudinally from the center point of said die face, together with a holding shoe co-operating with the members and spaced longitudinally from one end of the stiff back and engageable with a pipe on the side thereof to be engaged by the stiff back and force applying means joined to the stiff back adjacent each of said end portions and operative to move the stiff back into pipe clamping relation against said die face and thereafter to rock the stiff back for progressively bending the pipe along the die face; the improvement in said force applying means which comprises a pressure fluid responsive motor device connected with the stiff back end portion between said central point of the die face and said holding shoe, a pressure fluid delivery connection with said device and pressure relief means in said delivery connection responsive to selected back pressure therein for lessening force application on the stiff back at its last mentioned end portion for a back-off action thereon as the application of force continues on the other end portion for the rocking action of the stiff back.

2. In pipe bending machine, a relatively long and longitudinally straight stiff back engageable with a pipe along one side thereof, a fixed die having a longitudinally curved pipe conforming face engageable with the opposite side of the pipe in opposing relation to one relatively short length end portion of the long stiff back, a

holding shoe positioned in longitudinally spaced apart relation to said one end portion of the stiff back and engageable with the side of the pipe to be engaged by the stiff back and force applying means active on the stiff back for bending pipe on the curved die and comprising fluid pressure responsive mechanism having bearing on said one end portion of the stiff back at a point spaced from the longitudinal center of the pipe engaging face of the die in the direction toward said holding shoe, a force transmitting connection with the stiff back for rocking the stiff back about said bearing thereon of the fluid pressure responsive mechanism, a fluid pressure delivery conduit communicating with the fluid pressure responsive mechanism and means to relieve the application of pressure on the pressure responsive mechanism for accommodating back-off of its bearing on said one end portion of the stiff back during rocking progression of the stiff back in bending a length of pipe into conformity on the curved face of the die.

3.. In a pipe bending machine, a pair of longitudinally spaced apart pipe supports on which a pipe can be rested before and after a bending operation, a holding shoe and a relatively long and straight stiff back positioned between said supports in longitudinally spaced apart relation and both provided with power actuated means for their elevation in lifting a pipe above said supports and a bending die fixedly located above a relatively short length portion of the stiff back at its end which is near the holding shoe and provided on its underside with a longitudinally curved face against which a pipe is to be progressively pushed into conformation with the face curve, said power actuated means including a shiftable wedge mounted for slide reciprocation under the holding shoe, a first pressure fluid responsive motor operatively connected with the Wedge, a second pressure fluid responsive motor operatively connected to said short length portion of the stiff back at a point between the holding shoe and the longitudinal midpoint of the bending die, a third pressure fluid responsive motor operatively connected with the stiff back at a point spaced from said midpoint in a direction away from said holding shoe, pressure fluid supply valves controlling delivery of pressure fluid to said motors and a pressure relief valve in the pressure fluid connection to the second pressure fluid responsive motor and operative to accommodate descent of said point with the short length portion of the stiff back and away from said point during progressive rise of the point of connection of the third pressure responsive motor with the stiff back.

4. In a pipe bending machine as in claim 3, said holding shoe having a semicircular pipe seating face with close fitment with the pipe underside, a pair of arcuate clamping arms hinged to the holding shoe and power means to swing said arms into bearing fitment with the upper side of a pipe for co-operation with the holding shoe in pressing on the encircled pipe throughout substantially its circumference to resist out-of-round stressing thereon while an adjacent pipe portion is being bent.

5. In a pipe bending machine as in claim 4, said power means to swing the clamp arms including a fourth pressure fluid responsive motor connected in parallel with said second pressure fluid responsive motor for joint response therewith and a pressure fluid control valve operable to shut off pressure fluid delivery to said fourth pressure fluid responsive motor.

6. In a pipe bending machine, a pipe engageable holding shoe having clamp means co-operating therewith for embracing and stiffening a pipe positioned in the holding shoe, pressure fluid responsive means operably connected with the clamp means to close the same, a relatively long and straight pipe engageable stiff back in longitudinally spaced and aligned relation with the holding shoe, a bending die having a longitudinally curved pipe engaging face in opposing relation with a relatively short portion of the stiff back adjacent the end of the stiff back near the holding shoe, pressure fluid motors connected with portions of the stiff back respectively forward and rearward of the center of the bending die, pressure fluid supply connections joined to said motors in parallel relation for the application of force to move the stiff back into pipe contact with the bending die and to impart rock action of the stiff back for bending the pipe to die face curvature and a pressure fluid connection to the clamp operating pressure responsive means joined thereto in parallel and for conjoint operation with the pressure fluid motor which is connected with the stiff back portion rearward of the center of the bending die and adjacent the holding shoe.

7. In a pipe bending machine as in claim 6, a pressure relief valve in the pressure fluid supply connection to the last mentioned pressure fluid motor operative for maintaining a pressure level which accommodates back and forth movement of the forward stiff back portion throughout a progressive rocking of the straight stiff back to the end of its pipe bending action.

8. In a pipe bending machine as in claim 7 and a valve in the pressure fluid connection to the clamp operating pressure responsive means operative to shut off the delivery of pressure fluid and render the clamp ineffective.

9. In a pipe bending machine comprising the combination of:

a frame;

a die supported by said frame and having a curved face for engagement with a side of a section of pipe to be bent, which side is to form the inside are of the bend in said pipe;

a rigid longitudinally straight stiff back member adapted for supporting in frictional engagement on the opposite side of said pipe from said die, which side is form the outside arc of the bend in said pipe, said member extending longitudinally forwardly;

support means longitudinally spaced rearwardly from said die and positioned adjacent to the same side of said pipe as said stiff back member for supporting said pipe at least during the bending operation;

power means connected to said stiff back member for moving said stiff back member against said pipe and thereby exerting a pipe bending force in the general direction of the side of said pipe against which said die is positioned;

restraining means connecting said die and the rearward end of said stiff back member for restraining the increase in transverse spacing therebetween during exertion of force by said power means, said restraining means including payout means for increasing said transverse spacing when the separating force transmitted by said pipe from said power means exceeds a predetermined level.

10. The invention as claimed in claim 9 wherein:

said restraining means includes hydraulic cylinder and piston means connected to restrain separation of said die and the rearward end of said stiff back member and including relief means for relieving pressure in said cylinder means when said separating force exceeds the relief force of said valve means.

11. The invention as claimed in claim 9 including:

shiftable wedge means mounted for sliding reciprocation under said support means for varying the transverse spacing between said support means and said die during successive bending steps caused by actuation of said power means.

12. The invention as claimed in claim 11 including:

second power means for reciprocating said wedge means at predetermined times.

13. The invention as claimed in claim 12 wherein:

said second power means includes hydraulic cylinder and piston means connected to said wedge means and including second valve means for locking fluid in said cylinder means whereby said wedge means are locked in a fixed position relative to said support means.

References Cited UNITED STATES PATENTS 2,347,593 4/1944 Cummings 72-388 2,724,669 11/1955 QHill'OlO et a1. 72-381 Reif 72-682,

Roderick 7238 1 Cummings 5 72382 Lang 72-689 CHARLES W. LANHAM, Primary Examiner.

R. D. GREFE, Assistant Examiner. 

1. IN A PIPE BENDING MACHINE HAVING A PAIR OF MEMBERS PROJECTED LONGITUDINALLY OF A PIPE TO BE RECEIVED BETWEEN THE MEMBERS, ONE MEMBER PRESENTING A PIPE ENGAGING THE DIE FACE CURVED LONGITUDINALLY AND OUTWARDLY FROM THE CENTER POINT THEREON FOR PIPE BEND CONFORMATION THERETO AND THE OTHER MEMBER BEING A LONGITUDINALLY STRAIGHT STIFF BACK HAVING ITS OPPOSITE END PORTION SPACED IN OPPOSITE DIRECTIONS LONGITUDINALLY FROM THE CENTER POINT OF SAID DIE FACE, TOGETHER WITH A HOLDING SHOE CO-OPERATING WITH THE MEMBERS AND SPACED LONGITUDINALLY FROM ONE END OF THE STIFF BACK AND ENGAGEABLE WITH A PIPE ON THE SIDE THEREOF TO BE ENGAGED BY THE STIFF BACK AND FORCE APPLYING MEANS JOINED TO THE STIFF BACK ADJACENT EACH OF SAID END PORTIONS AND OPERATIVE TO MOVE THE STIFF BACK INTO PIPE CLAMPING RELATION AGAINST SAID DIE FACE AND THEREAFTER TO ROCK THE STIFF BACK FOR PROGRESSIVELY BENDING THE PIPE ALONG THE DIE FACE; THE IMPROVEMENT IN SAID FORCE APPLYING MEANS WHICH COMPRISES A PRESSURE FLUID RESPONSIVE MOTOR DEVICE CONNECTED WITH THE STIFF BACK END PORTION BETWEEN SAID CENTRAL PORTION OF THE DIE FACE AND SAID HOLDING SHOE, A PRESSURE FLUID DELIVERY CONNECTION WITH SAID DEVICE AND PRESSURE RELIEF MEANS IN SAID DELIVERY CONNECTION RESPONSIVE TO SELECTED BACK PRESSURE THEREIN FOR LESSENING FORCE APPLICATION ON THE STIFF BACK AT ITS LAST MENTIONED END PORTION FOR A BACK-OFF ACTION THEREON AS THE APPLICATION OF FORCE CONTINUES ON THE OTHER END PORTION FOR THE ROCKING ACTION OF THE STIFF BACK. 